Ceramic insulating material



ounce STATES PATENT omen.

JOSEPH A. JHIEBY, OF DETROIT, MICHIGAN, ASSIGNOR TO JEFFEBY-DEWITT COMPANY, OF DETBOIT, MICHIGAN, A CORPORATION OF MAINE.

CERAMIC INSULATING MATERIAL.

Be it known that I, JOSEPH A. JEFFERY, a

citizen of the United States, and a resident of Detroit, in the county of \Vayne and State of Michigan, have made an Invention Appertaining to Ceramic Insulating Materials, and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

My invention relates to the production of a ceramic material and the raw batch thereof. The invention particularly has for its object to provide an insulating material of the porcelain type, which has hi h electrical resistance at atmospheric and igher temperatures and at the same time possesses the following additional valuable roperties: An exceptionally high mechamcal strength, a vitreous structure throughout the mass, a low coefiicient of thermal expansion, a high specific gravity, a high modulusrof elasticity, a high thermal conductivity, a low specific heat and maximum physical and chemical homogeneity.

By reason of these properties the articles composed of the material embodying my invention are exceedingly valuable when used as insulators under conditions where a considerable resistance to impact, compress10n, tension, vibratlon, and other mechanical strains, imperviousness to liquids'and gases,

and resistance to changes, .are required.

The material of my inventlon is parsudden temperature 'ticularly valuable where the articles composed thereof are subjected to electrical stresses at high temperatures and to sudden and wide changes of temperature, since the material has a high dielectric strength over a wide range of temperature, a low thermal expansion;'and hence may be subjected to the said conditions without serious clec-. trical leakage or mechanical breakage of the insulator. My invention thus is of value i when applied to insulators for spark plugs used in internal combustion engines, which require a high hot dielectric,- strength, a high mechanical strength, a high thermal diffusivity, and a low coeflicient of thermal expansion to efficiently perform their functions,

lnsulatorsiof the porcelain type gen- Specification of Letters Patent. Patented lu 21 1922;

1920. Serial No. 381,637.

eral use do not possess the property of high dlelectric strength at high temperatures because i of the use of comparatively large amounts of feldspar, or other alkali metal compounds, as fluxes in the raw batch, which introduces a corresponding amount of one or more alkalies into .the mixture. Consequently, the electrical resistance of such insulators decreases rapidly as the temperature increases. They do not possess the property of exceptionally high mechanical strength or of maximum physical stability because of a relatively low specific gravity, a low modulus of elasticity and indefinite chemical and physical homogeneity. They do not possess the property of exceptionallyinsulator, Well known in the art, I have overcome as follows: First, by using, in compounding the raw batch of the bod the alkaline earth oxides as the principal uxes. These may be introduced in the form of mineraloglcal or raw compounds as talc or through definite, hard calcined, vitrified or fused minerals or through definite, hard calcined, vitrified or fused synthetic compounds as sources. compounding the raw batch of the body, one

Second, by using, in

or more chemically and mineralogically= definite, dense and stable raw.const1 tuents such as the mineral sillimanite or chemically and mineralogically definite, hard, calcined, vitrified or fused natural, or synthetic constituents of such compounds prepared by prefiring, in such proportions that with the minimum amount of raw clays, consisting of kaolin alone or a mixture of kaolin and ball clays in proportions necessary for plasticity and practical working propertles. or a calcined mixture of clay, alumina and an alkaline earth metal flux compound with raw clay, that on firing the body to the required temperature to vitrify the mass,

definite endproducts are formed and a maximum amount of sillimanite is'produced, causing the resulting materlal to be prac-t tically in chemical and physical equilibria controlled in the following and of maximum .density, both apparent and true.

Raw materials, other than clays, which increase in density upon firing or by pyro chemical reaction with the other constitu'' ents, may be usedl The amount of hard calcined, vitrified or fused natural or synthetic material, or of dense, stable, hard natural minerals of the same physical characteristics, used, is governed by the use for which the roduct is intended and the properties, or t sin degrees, which it is desired to secure in the final product. I

The quality ofJthe final product may be .Way: 1. Increase of the hot dielectric stren h and the toughness of thebody are broug t about byincreasing the alkaline earth metal content and decreasing the alkalimetal content in the final body composition; 2. RGSlSt-EIICG to sudden temperature changes resulting from final body. composition a low coeflicient or thermal ex ansion of the body is brought about by a high content of sillimanite or other inert material inthe 3..The densitg of the body is controlled by the quality 6 the sillimanite and its amount with respectto the glassy-matrix. All the above ualities are controlled not only by the c emical composition of the final product but alsoby "magnesia either 'the artificial hydrate or.

mineral 'ydrate, brucite, talc, and other magnesium .complounds yielding the oxide or a on eatin 5 whitin or other calciumicarbonatw, ca cium oxi e, calcium hydrate, and other calcium compounds yielding the oxide or a silicate onheating; dolomite or other mixed calcium and maglnesium i 7 resulting carbonate, dolomitic oxide, dolomitic ydrate and other mixed calcium and magnesium compounds yieldin the oxides or: sillcates on heating; or bery ium, barium, stront um, lithium and other alkaline earth metal comunds yielding the oxide or a silicate on eati Whi eboth metal oxides may be used as fluxes, the former, roducing alkali metalsihcaites 1n the 7 material upon firing, seriously reduce the dielectric strengthyof the final product at high temperatures;n The maxi-' t6 mum amount of the oxides of the alkaline alkali metal and alkaline-earth :of a mixed synthetic silicate of the last earth metals, or their equivalents, and the minimum amount of the oxides of the alkali metals, or their equivalents, possible, are used, in order to secure the requisite properties desired to be'produced in the material resulting. after firing, particularly as to the hot dielectric stren h and resistance to sudden temperature 0 anges. The exact proportion of one to the other will be governed y the use for which the final product is intended and the properties, or their degrees, which it is desired to secure in the article to be produced, and this proportion is particularly" overned by the firing conditions commerclally feasible 1n the ceramic art. The total amount of fluxing oxides used is determined by the chemical composition and the amount of the calcine selected to constitute the flux of the bodybatch. They will vary from about 4% to about 10% of the body batch.

In com ounding, previous to pre-firing,

the material which is either to' constitute or to contain the sillimanite of the body batch, the raw materials used are calculated in definite proportions to produce, on firing to the proper temperature, either synthetic sillimanite alone or a selected definite silicate which will contain adefinite amount of synthetic sillimanite togetherwiththe flux so that there will be preferablyincorporated in the raw batch about/10% to about 50% ofsilliinanite. For-example, if a calcine is 'to be employed which consists wholly of ,sillimanite the calculated raw batch for this calcine will be 258 parts of 'kaolin and 102 parts of anh drous aluminum oxide, or 258 parts of kao in and 156 parts of hydrated aluminum oxide. Instead of synthetic sil limanite, the natural minerals silliruanlte, andialusite and cyanite or kyanite may be use w In compounding the raw body batchpreparatory toforming and firing the articles in their final shapes, the nonplastic material is preferably ground and mixed with other materials, mostly clays. The nonplastic material is' formed of one or. more chemically, mineralogically, definite, dense and stable raw constituents like sillimanite,

andalusite and c anite and of chemically and mineralogical y definite, hard, calcined, vitrified or fused natural or synthetic constituents like sintered or fused magnesium oxide; or it is formed of a 'mixture of raw or; it is formed of synthetic sillimanite (Al O,.SiO,-) andsynthetic silicates of the form XMgO.YAl O,.ZSiO,; or it is formed two named.

kaolin, bauxite, diaspora or similar material and alumlna suflicient 1n amount'to The balance of the mixture consists chiefly of clays. It may be formed of kaolin alone or. a mixture of kaolin and ball clays, the latter being added for plasticity and eneral working properties of the raw body. t is, however, preferable to use a clay or a clay mixture that will mature at about the temperature at which the body containing the nonplastics and the plastics will mature in the firing. I find it preferable to use a mixture of Edgars plastic clay in as large amount as .the manufacturing conditions will permit one or more ball clays such as Johnson & orter ball clays to increase the plasticity and the proper working quality, and a suitable amount of china clay, such as Harris clay, to make up the balance of the raw clay content. I have selected Edgars plastic kaolin as the type of kaolin that'I preferably use. A description of Edgars Elastic kaolin is given in the United States 'eological Survey Paper No. 11, pages 83-85, 1903. Likewise the Johnson & Porte:' ball clay is the ty e of the ball clay that I preferably use and isdescribed in the Tennessee ,Geological Survey Bulletin No. 5,

pages 85-87, 1910. Also the Harris clay is Table No. 1.

Collected Raw batch for combined 5 that; simmanite and Raw bath g g body Calculated end products in fired body. gg f 5% Cone 18. on basi;

E.p.kaolin 71.2 i AlzOzfiHzO C3filI63d4SxAlz03SlOgYMgO. 58. 24 Sillimanite. 38. 80 63.16 66. 8

. l Talc Feld spiir 2. 91 Glass matrix. 31. as as. 2

Johnson & Porter ball clay (raw) 9. 72 Sillimanite. Harris clay (raw) 9. 72 Si E. p. kaolin (raw) 19. 41 E20 driven out 5. 46

Table No. 2.

- F Collected Raw batch oi the bgdyl Calculated endggplcqcts 1n fired body. cqljlpgltsed tpolsaylj basis.

Natural mineral sillimanite auoasioz. 44. 0 74. 19. 9o 512 18.75 20. 1o

. 2. 5 Sillimanite all clay 9. 0 H O (driven out).... Raw Hams cla 9.0 Silica Raw Edgars plastic kaolin 30. 3

atype of china clay that I find preferable and it is. described in the United States Bureau of Mines, Bulletin No. 53, pages 150151, 1913. A small amount of flux, such as feldspar, is preferably added to the clay mixture to control the texture of the required temperature to thoroughly vitrify the mass and allowing proper time for the pyrochemical reactions to reach completion, cefinite end products are formed, causing the resulting material to be practically in chemical and physical equilibria and of maximum density, both apparent and true.

If the requisite conditions in the final product after firing, as hereinafter set forth, are secured, itis immaterial whether one or more than one calcine or natural mineral, or a mixture of calcines and natural minerals as discussed above, are used to make up the non-plastic portion of the body batch.

Examples of possible compositions based on the principles just discussed, and designed to produce the hereinafter stated requisite conditions in the final product, are given in the following tables:

These compositions when suitably prepared in the raw batch by the usual processes known to the art. The milling operation, however, should be sufiicient to give theproper homogeneity for the purpose for which the body is intended.

the body composition and it is understood that these changes may be made without departing from the spirit of my invention. It

is, however, preferable that the glaze-be so composed as to fit the body-composition rather than that the body composition be materially altered. The glaze-may be applied to the raw or to the bisque body acmass, impervious to liquids and used, dense, but lightly bonded and friable bodies, which are exceptionally rapid cutting by any means of dry-forming known to the art.

The proportions of the constituents, both raw and calcined, or of their equivalents, used in compounding the raw body batch may be varied according to the method of 'manufacture and according to the properties, or their degrees, which are required in the resultant material of the insulator.-

As indicated in the tables, it is desirable to introduce a small amount of feldspar, in order that the crystallization of the sillimanite in the resultant material during firing and cooling may be controlled and thus improved. The feldspar may be introduced as indicated in the tables or through one of the synthetic silicates.- On account of its ing high cutting mentioned above. uents. being. themselves-physically dense detrimental effect on the resistivity at high temperatures as well as on other important properties of the body, it is used in the;

smallest amount possible. I

The final bodies produced by proper mani ulation and firing of thematerials of the ta les contain a large amount of sillimanite, a small amount'of lassy matrix'and a small amount of silica. .lhe sillimanite will vary from 60% to 85% according to the batch mixture and the firing conditions. More-' over, the silica that is derived from the'clay upon the formation out of the clay when the batches are fired are also small in amount and enters into solution or combination in "the glassy matrix, as for instance, in table No. 2 the silica from the raw clay is only 11.25% which in the final body is 12.2%. This ma increase however if the firing is imper ect which would result in the production of less sillimanite in the final body.

The firing and manipulation is such that the silica thus derived does not exceed 17%.

The batches formed'by the compositions set forth in the tables given above, are particularly adapted to the ordinary process of plastic forming. When, however, the raw bodies are formed by casting processes, the raw batch is necessarily varied so as to per mit the requisite flow of water into the mold from the slip by the use of a short clay, such' as Harris clay. In order, however, to maintain the control of the maturing of the body in the firing and yet permit the proper removal of the water during the casting, dehydrated Edgars plastic clay is used. To maintain this control of the maturing of the body the largest amount of the calcined or dehydrated Itdgars plastic clay is used that is consistent with the working conditions existing in the casting process. The balance of the clay content is made up of the short clay or nonplastic clay which cooperates with the calclned clay to. permit the proper and continuous removal of the water from the body while in the mold, To control the .grain and texture of the final body, a slightly greater amount of feldspar is ordinarily required when the body is formed by the casting process. A composition particularly adapted for the casting process is illustrated in the following example:

Ta bleNo. 5.

Raw batch for combined Iyn- I thetie sillimanite and flux. Raw batccg for1 zhe body.

Total basis.

Collected Calculated and products in body. toms.

Calclned XLhOLSiOzYMgO AlgOgASiOx.

sillimanite ..'...l 40.00

Glassymatrix 23.75

sass

i as

The nonplastic constituents, either natural or synthetic, of the raw bodybatch, are used the drying and the as a means of controlling firing shrinkages and t e casting qualities.

'lheyincide'ntally provide a meansvof secur-. speed in dry-forming as hese nonplastic constit- -andhom0geneous, of high specific gravityand of definitechemioal composition, produoe, upon' mixing with suitable proportions of raw plastic constituents of definite chemical composition and firingto a suitable temperature under proper conditions, a physically dense and homogeneous final product, vitreous throughout the mass, of-high specific gravity, of exceptionally high mechanical stren of .a big thermal conductivity, of a high h, of a high modulus of elasticity,

hotv dielectric strength, of a low specific heat,

and one which is practically in chemical and physical equilibria.

By controlling the chemical and mineralogical composition of the raw body batch there is produced in the final product, after firing, the following requisite conditions 1. A maximum amount of sillimanite and a minimum amount of glassy matrix. 2. Alkaline earth metal silicates in excess of alkali metal silicates in the lassy matrix.

A minimum amount of silica, substantially all of which is in combination or in solution. 4. No elements or compounds in unstable form, or ones which will become unstable within the temperature range of the commercial use of the product. maximum chemical and physical equilibria. 6. A maximum density, both apparent and true.

This chemical control, therefore, results in a chemical composition which, coupled with the above stated physical properties, gives a final product having also, in the highest degree, the properties of high dielectric strength, or resistivity, at high temperatures under operating conditions as in a high speed, high compression internal combustion engine, and a mipimum coefficient of thermal expansion.

In order to obviate prolixity in the claims, I have specified in some parts of the specification and in some of the claims a single compound of a particular class, but it is to be understood that the claim covers and comprehends in each case one or more compounds of that class and that I may use a plurality of compounds of the class named and yet be operating within the scope of the claim in question. Also where I refer to the amount of the flux in the claims, I have reference to the amount of the flux compounds such as talc and feldspar as introduced originally even though the compounds are modified by prefiring andnot to basic oxides of the fluxing metals nor to the modifications produced by the prefiring. It is to be understood, however, that I contemplate covering in such claims equivalent fluxing constitutents whether claimed in the raw batch compositions or in the final product compositions.

I claim:

1. The rawbatch of a ceramic material comprising a mixture of sillimanite, a flux and a-clay mixture the clay content, when heated by itself, maturing at the temperature at which the ceramic body matures.

2. The raw batch of a ceramic material comprising approximately equal parts of clay and sillimanite and 4% to 10% alkaline earth metal and alkali metal'fiuxes.

3. The raw batch of a ceramic material comprising -a mixture of approximately I equal amounts of clay and sillimanite and from 4%"to-10% of flux formed of alkaline earth metal compound and alkali metal compound, the alkaline carth metal compound being in excess of the alkali metal compound.

4. The raw. batch of a ceramic material comprising a combined synthetic sillimanite and flux and a clay mixture the clay content,

7. The rawbatch of a ceramic material comprising clay and a combined synthetic sillimanite and alkaline earth metal compound, the clay content, when heated by itself, maturing at the temperature at which the ceramic body matures.

8. The raw batch of a ceramic material comprising clay, a combined synthetic sillimanite and alkaline earth metal compound, the clay content, when heated by itself, maturing at the temperature at wh1ch the ceramic body matures, and an alkali metal .compound. v

9. The raw batch of avceramic material comprising a combined synthetic sillimanite and about 4.5% of an alkaline earth metal compound, a claymixture and about 3% of alkali metal compound.

10. The raw batch of a ceramic material comprising a combined synthetic silicate consisting of sillimanite and flux anda clay mixture containing Edgars plastic kaolin, ball clay and china clay.

11. The raw batch of a ceramic material comprising a combined synthetic sillimanite and flux and a clay mixture containing Edgars plastic kaolin of about 20% of the batch and the remainder formed of ball clay and china'clay.

12. The raw batch of a ceramic material comprising a clay mixture and a combined synthetic sillimanite and flux formed of about of Edgars plastic-kaolin, about 20% of hydrated alumina and about 8% of an alkaline earth metal compound.

13L'The raw batch of a ceramic material comprising a clay mixture containing Edgars plastic clay, ball clay and chinaclay,

theclay content, when heated by itself, maturlng at the temperature at which the cera- IIllO'bOdY matures, and a combined synthetic .sillimanite and flux formed of about 70% of Edgars plastic kaolin, about 20% of hy-- drated alumina and about 8% of an alkaline earth metal compound.-

l i. The'raw batch of a. ceramic material v the clay content, when heated by itself, ma-

turing at the temperature at which the ceramic body matures.

15. The raw batch of a ceramic material I comprising about 20% of Edgars plastic consisting kaolln, about 10% of ball clay, about 10% of china cla and about 60% of a combinedsynthetic sillimanite and flux containing about 70% of Edgars plastic kaolin, about 20% of hydrated alumina and about 8% of talc.

. 16. The raw batch-of a ceramic material of about 19% of Edgars plastic kaolin, a out 10% of ballclay, about 10% of china cla about 3% of feldspar, and about 58 o a combined synthetic sillimanite and flux containing about 70% ofEdgars plastic kaolin, about 20% of hydrated alumina and about 8% of talc.

17. A raw batch {or a ceramic body comprisin ture t at when heated by itself matures at the temperature at which the ceramic body matures.

18. A raw batch for a ceramic'body comprising aluminous materials, a flux, and a clay mixture that when heated by itself matures at the temperature at which the' ceramic body matures. a

19. A ceramic material consisting of 60% to 85% of sillimanite and the balance of 7 ceramic materials and a-clay mix maniteand a glassy matrix, the silica derived from the clay upon the formation'sof sillimanite from the clay not'exceeding 17 of the content of the material.

22. The process of forming a ceramic body which consists in forming a raw batch of aluminous materials, flux and a clay mixture that when heated by itself will mature at the temperature at WhlCll the ceramic body matures heating he cla mixture.

23. he process of forming a ceramic body which consists in forming a raw batch of aluminous materials, flux and a clay mixture that when heated by itself will mature at the temperature at which the ceramic body matures" eating the raw batch to maturity of the clay mixture to form sillimanite from.

the clay and a lassy matrix that will dissolve substantia v allthe silica that splits from the clay in the formation of sill'imanite from the clay.

In testimony whereof I have hereunto signed my name to this specification.

JOSEPH A. J EFFERY.

the raw batch to maturity of 

